Bladderwrack

Bladderwrack is generally safe, though there are three potential problems with its consumption: acne, thyroid dysfunction, and heavy-metal contamination. Iodine in any form—including from bladderwrack and other seaweeds—can cause or aggravate acne in some people.²⁷ Excessive iodine ingestion can cause either hypothyroidism or hyperthyroidism and should be avoided.^{28, 29} Bladderwrack and other seaweeds that grow in heavy-metal-contaminated waters may contain high levels of these toxins (particularly arsenic and lead), leading to nerve damage,³⁰ kidney damage,³¹ or other problems. Only bladderwrack known to have been harvested from clean water or labeled to indicate the absence of heavy metals or other contaminants should be consumed. The safety of using bladderwrack during pregnancy and breast-feeding is unknown. People who are allergic to iodine may need to avoid bladderwrack.